BigDaddy0363

First time poster but have used the site for many problems. I need help trying to figure out why my 2000 GT looses power in 4th and 5th gears with a hard acceleration. First the back story. I replaced the motor with a reman. last summer. Along with that was the new plugs, filter, and fuel pump. I've resently started driving it daily to start breaking it in. Normal driving there is no problem what so ever. But when i take it on the x-press way and I'm in 4th gear I can get the car up to 70 and can milk it to 80 but when I try and hard accelerate it looses power and when I shift into 5th I can get it up to 70 and do the same thing and it looses power until I let off the gas. When I'm driving around town and hard accelerate in 1st, 2nd, or 3rd gears the car responds with no problems. I've changed the Idle Position Sensor already. Didn't help. Don't want to start replacing sensors that don't need to be replaced. Any help would be great. Thanks.

ticopowell

It almost sounds like it has a speed limiter on it.. but if it's a 2000 then I wouldn't think it had anything like that. It also could be a traction control issue... But these are just guesses, possibly a good place to start looking but I really can't help much more than that.
Have you checked for DTC's?

JC316

What brand of fuel pump did you use? I would check for codes, check the fuel pressure, and check the air filter. You might have a rats nest clogging up the air filter if it's been sitting.

BigDaddy0363

Sorry for taking so long to reply, work gets in the way. So I thought that I had changed the air filter when I installed the new motor. Must have just blew it out and put it back in. But I disconnected the maf sensor and the iat sensor and removed and replaced the air filter. After doing that and plugging the sensors back in car is running at 100%. Just can't believe the air filter was that bad it influenced the hp at the higher speeds. So whether it was one of the sensors not making the proper connection or a bad air filter, car is fine. Thanks for everyone's help. On to the next project.

BigDaddy0363

Well here's the update. After less than 24 hours after changing the air filter the problem came back. Wasn't betting on the air filter fixing the problem. So I did a little experiment, I unpluged the MAF and the problem reversed, no power starting off but could hammer it in 4th and 5th with no stalling. That lasted about 30 mins. then it went down hill thru all gears and power bands. Removed the MAF and cleaned it, no improvement. Went out and bought a new one and installed. The problem is still there but at a higher speed before it looses power when I hard accelerate. So, the PCM is controlling all this thru relays and fuses right. Can a relay be partially bad. I'm truly stupped. Can't be fuel pump or fuel delivery, I've had the car running good for at least 12 hours. Any help would be great. Thanks.

ticopowell

I assume you checked for codes, one about the MAF missing should have popped up at least.
I wonder if the wires to the MAF are damaged, or any wires out of the PCM for that matter... could be that when they get hot they don't like the higher speeds.
Just bouncing ideas, good luck, sorry you still are having issues.

BigDaddy0363

Here's the lastest update. Disconnected the battery and let it sit overnight. Reattached the battery cable and went through the drive cycle. Went to AutoZone and had it read for codes. All systems checked out and there were no codes. As I was driving to work I was milking the gas it 5th gear to get to 80 and was holding steady. Then all of a sudden the car lost all power, the check engine light started flashing, and it dropped down to 35 mph. I had to work the gas pedal to keep it from dying. Pulled over to the side of the road and it died. Let it set for about 3 mins and started it back up. You could still feel the car isn't at full power but is drivable during normal conditions. I'm completely out of ideas. Really need some up on this. I really dont want to take this to the dealer. I know I'll get raped. HELP!!!!!!!

ticopowell

I would check for codes again, see what popped up if anything.

Other than that I really don't have any idea what could be wrong... Could it be a bad PCM?
Do you know any mechanics you trust?
I sure hope someone else chimes in again, sorry I'm not all that much help :/

BigDaddy0363

Went to AutoZone again to have the codes checked and again no codes came up. I have raised the white flag and took the car to a dealer. When I get the results back from them Ill pass it on to everyone on here. Thanks for all the help. This one is a brain teaser.